Just in case the humour police swing by, the above was mostly Tongue in cheek. I actually have a lot of respect for sports jackets.

I'd suggest you're up front and honest with them, mention it being the dream of a lifetime and something you need to do whilst still able. Surely there's some science related experiment you can combine with it? Get the education board and governors seeing it as an opportunity rather than a problem of how to fill your vacancy?

If it's around the same time as school budget review the head might be grateful of a way to temporarily reduce the salary cost?